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Noise in the engine

i have a j30 infiniti with 220,000 miles. When i start it up it has a raddling sound on the top end and can’t figure it out. Sound goes away as i accelerate comes back at idle. I have heard there j30’s with the same sound. Could it be a bad injector

j30, Infinity . . .
Model-Year ?
CSA

Injectors generally don’t rattle. It could be in the valve gear when the oil drains out overnight and there is metel to metal contact when you start up in the morning. As the valve sytem pressures up with oil, the rattle would disappear.

It needs a good mechanic to track down your noise.

Is it a serious condition and is it a costly one

It is a 1996 j30 infiniti

Is Your Cooling Fan Mounted To The Water Pump Flange ? I’d Check That. It Has Caused These Symptoms On 96 J30s. Carefully (Fans Are Dangerous. They Can Bite You, Come Off, Or Shed Blades.) Observe The Fan For Wobbling Or Flapping While Idling.

Use a length of hose, one end to your ear, the other as probe, to explore non-moving engine parts to isolate the sound. Better yet, 10 or 15 bucks will buy you an automotive stethoscope - stereo ! BE CAREFUL.

CSA